Heavily armed Greek forces with their firearms drawn forced a Gaza-bound ship to turn around and return to Greece, where the vessel is now being held in a military base, activists on board the Audacity of Hope said Friday evening.

"We were forced to go back to a Greek port surrounded with bars and barbwire," a Twitter message from the Gaza-bound vessel said. "We were in a holding pattern for probably three hours when the commandos arrived with drawn weapons."

Hagit Borer, an Israeli-American citizen on the ship, told Ynet: "They are not letting us out. They took us back to a military dockyard and let the journalists disembark. I don't know what they'll be doing with us."

Describing the takeover of the vessel, Borer said: "They arrived with machine guns. It was quite scary. They seemed ready for a fight. The commandos looked threatening, they wore helmets and their faces were covered."

The ship, which is carrying some 50 American and Israeli activists, journalists and crewmembers, left its Greek port without authorization earlier Friday, only to be intercepted Coast Guard some 25 minutes later.

Later Friday, Hamas condemned Greece over its actions. The interception of the boat was "inhumane" and contradicted international laws, a statement by Hamas' leadership in Damascus said.

The Audacity of Hope setting sail (Photo: Reuters)

'Greeks doing Israel's dirty work'

Greek forces were apparently attempting to convince the vessel to turn around, before forcing its crew to head back to Greece. Coast Guard "commandos" were pointing their weapons at the vessel during the ordeal, activists said.

"The boat is moving back to port, flaked by two zodiacs and one Greek Coast Guard ship full of commandos," another Twitter message said. "So sad that the Greeks are doing the dirty work of Israel by not letting us sail."

Passangers who stayed in Athens (Photo: Reuters)

"I never knew the Mediterranean was owned by Israel," another activist said.

Spirits on the vessel were high earlier, with one activist saying: With great joy we left Parama pier. Under bright blue sky…" Activists kept their spirits up even as their boat was stopped by Greek forces, with one message reading: "As commandos point their weapons, passengers are singing 'we shall overcome' in the middle of the Athens Sea."

The Greek embassy in Israel released the following announcement on behalf of Greece's Ministry of Citizen Protection earlier Friday.

"Pursuant to a decision by the Minister of Citizen Protection Mr. C. Papoutsis, the departure of ships with Greek and foreign flags from Greek ports to the maritime area of Gaza has been prohibited today."

The Greek officials Ynet spoke with Friday evening were unable to confirm or deny that the Gaza-bound vessel was returned to port by armed forces.